Assembly Language for x 86 Processors 7 th

Assembly Language for x 86 Processors 7 th Edition Kip R. Irvine Chapter 8: Advanced Procedures Slides prepared by the author. Revision date: 1/15/2014 (c) Pearson Education, 2015. All rights reserved. You may modify and copy this slide show for your personal use, or for use in the classroom, as long as this copyright statement, the author's name, and the title are not changed.

Chapter Overview • • • Stack Frames Recursion INVOKE, ADDR, PROC, and PROTO Creating Multimodule Programs Advanced Use of Parameters (optional) Java Bytecodes (optional) Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 2

Stack Frames • • • Stack Parameters Local Variables ENTER and LEAVE Instructions LOCAL Directive Write. Stack. Frame Procedure Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 3

Stack Frame • Also known as an activation record • Area of the stack set aside for a procedure's return address, passed parameters, saved registers, and local variables • Created by the following steps: • Calling program pushes arguments on the stack and calls the procedure. • The called procedure pushes EBP on the stack, and sets EBP to ESP. • If local variables are needed, a constant is subtracted from ESP to make room on the stack. Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 4

Stack Parameters • More convenient than register parameters • Two possible ways of calling Dump. Mem. Which is easier? pushad mov esi, OFFSET array mov ecx, LENGTHOF array mov ebx, TYPE array call Dump. Mem popad Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. push call TYPE array LENGTHOF array OFFSET array Dump. Mem 5

Passing Arguments by Value • Push argument values on stack • (Use only 32 -bit values in protected mode to keep the stack aligned) • Call the called-procedure • Accept a return value in EAX, if any • Remove arguments from the stack if the calledprocedure did not remove them Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 6

Example . data val 1 DWORD 5 val 2 DWORD 6. code push val 2 push val 1 (val 2) (val 1) 6 5 ESP Stack prior to CALL Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 7

Passing by Reference • Push the offsets of arguments on the stack • Call the procedure • Accept a return value in EAX, if any • Remove arguments from the stack if the called procedure did not remove them Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 8

Example . data val 1 DWORD 5 val 2 DWORD 6 (offset val 2) (offset val 1) . code push OFFSET val 2 push OFFSET val 1 Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 00000004 0000 ESP Stack prior to CALL 9

Stack after the CALL value or addr of val 2 value or addr of val 1 return address Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. ESP 10

Passing an Array by Reference (1 of 2) • The Array. Fill procedure fills an array with 16 -bit random integers • The calling program passes the address of the array, along with a count of the number of array elements: . data count = 100 array WORD count DUP(? ). code push OFFSET array push COUNT call Array. Fill Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 11

Passing an Array by Reference (2 of 2) Array. Fill can reference an array without knowing the array's name: Array. Fill PROC push ebp mov ebp, esp pushad mov esi, [ebp+12] mov ecx, [ebp+8]. . ESI points to the beginning of the array, so it's easy to use a loop to access each array element. View the complete program. Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 12

Accessing Stack Parameters (C/C++) • C and C++ functions access stack parameters using constant offsets from EBP 1. • Example: [ebp + 8] • EBP is called the base pointer or frame pointer because it holds the base address of the stack frame. • EBP does not change value during the function. • EBP must be restored to its original value when a function returns. 1 BP in Real-address mode Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 13

RET Instruction • Return from subroutine • Pops stack into the instruction pointer (EIP or IP). Control transfers to the target address. • Syntax: • RET n • Optional operand n causes n bytes to be added to the stack pointer after EIP (or IP) is assigned a value. Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 14

Who removes parameters from the stack? Caller (C) push val 2 push val 1 call Add. Two add esp, 8 . . . or. . . Called-procedure (STDCALL): Add. Two PROC push ebp mov ebp, esp mov eax, [ebp+12] add eax, [ebp+8] pop ret ebp 8 ( Covered later: The MODEL directive specifies calling conventions ) Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 15

Your turn. . . • Create a procedure named Difference that subtracts the first argument from the second one. Following is a sample call: push 14 push 30 call Difference ; first argument ; second argument ; EAX = 16 Difference PROC push ebp mov ebp, esp mov eax, [ebp + 8] sub eax, [ebp + 12] pop ebp ret 8 Difference ENDP ; second argument ; first argument Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 16

Passing 8 -bit and 16 -bit Arguments • Cannot push 8 -bit values on stack • Pushing 16 -bit operand may cause page fault or ESP alignment problem • incompatible with Windows API functions • Expand smaller arguments into 32 -bit values, using MOVZX or MOVSX: . data char. Val BYTE 'x'. code movzx eax, char. Val push eax call Uppercase Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 17

Passing Multiword Arguments • Push high-order values on the stack first; work backward in memory • Results in little-endian ordering of data • Example: . data long. Val DQ 1234567800 ABCDEFh. code push DWORD PTR long. Val + 4 push DWORD PTR long. Val call Write. Hex 64 Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. ; high doubleword ; low doubleword 18

Saving and Restoring Registers • Push registers on stack just after assigning ESP to EBP • local registers are modified inside the procedure My. Sub PROC push ebp mov ebp, esp push ecx push edx Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. ; save local registers 19

Stack Affected by USES Operator My. Sub 1 PROC USES ecx edx ret My. Sub 1 ENDP • USES operator generates code to save and restore registers: My. Sub 1 PROC push ecx push edx pop ecx ret Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 20

Local Variables • Only statements within subroutine can view or modify local variables • Storage used by local variables is released when subroutine ends • local variable name can have the same name as a local variable in another function without creating a name clash • Essential when writing recursive procedures, as well as procedures executed by multiple execution threads Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 21

Creating LOCAL Variables Example - create two DWORD local variables: Say: int x=10, y=20; ret address saved ebp EBP 10 (x) [ebp-4] My. Sub PROC 20 (y) [ebp-8] push mov sub ebp, esp, 8 mov DWORD PTR [ebp-4], 10 ; initialize x=10 DWORD PTR [ebp-8], 20 ; initialize y=20 Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. ; create 2 DWORD variables 22

LEA Instruction • LEA returns offsets of direct and indirect operands • OFFSET operator only returns constant offsets • LEA required when obtaining offsets of stack parameters & local variables • Example Copy. String PROC, count: DWORD LOCAL temp[20]: BYTE mov lea edi, OFFSET count esi, OFFSET temp edi, count esi, temp Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. ; ; invalid operand ok ok 23

LEA Example Suppose you have a Local variable at [ebp-8] And you need the address of that local variable in ESI You cannot use this: mov esi, OFFSET [ebp-8] ; error Use this instead: lea esi, [ebp-8] Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 24

ENTER Instruction • ENTER instruction creates stack frame for a called procedure • • pushes EBP on the stack sets EBP to the base of the stack frame reserves space for local variables Example: My. Sub PROC enter 8, 0 • Equivalent to: My. Sub PROC push ebp mov ebp, esp sub esp, 8 Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 25

LEAVE Instruction Terminates the stack frame for a procedure. Equivalent operations My. Sub PROC enter 8, 0. . leave ret My. Sub ENDP push ebp mov ebp, esp sub esp, 8 ; 2 local DWORDs mov pop Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. esp, ebp ; free local space ebp 26

LOCAL Directive • The LOCAL directive declares a list of local variables • immediately follows the PROC directive • each variable is assigned a type • Syntax: LOCAL varlist Example: My. Sub PROC LOCAL var 1: BYTE, var 2: WORD, var 3: SDWORD Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 27

Using LOCAL Examples: LOCAL flag. Vals[20]: BYTE ; array of bytes LOCAL p. Array: PTR WORD ; pointer to an array my. Proc PROC, LOCAL t 1: BYTE, ; procedure ; local variables Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 28

LOCAL Example (1 of 2) Bubble. Sort PROC LOCAL temp: DWORD, Swap. Flag: BYTE. . . ret Bubble. Sort ENDP MASM generates the following code: Bubble. Sort PROC push ebp mov ebp, esp add esp, 0 FFFFFFF 8 h. . . mov esp, ebp pop ebp ret Bubble. Sort ENDP Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. ; add -8 to ESP 29

LOCAL Example (2 of 2) Diagram of the stack frame for the Bubble. Sort procedure: Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 30

Non-Doubleword Local Variables • Local variables can be different sizes • How created in the stack by LOCAL directive: • 8 -bit: assigned to next available byte • 16 -bit: assigned to next even (word) boundary • 32 -bit: assigned to next doubleword boundary Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 31

Local Byte Variable Example 1 PROC LOCAL var 1: BYTE mov al, var 1 ret Example 1 ENDP Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. ; [EBP - 1] 32

Write. Stack. Frame Procedure • Displays contents of current stack frame • Prototype: Write. Stack. Frame PROTO, num. Param: DWORD, ; number of passed parameters num. Local. Val: DWORD, ; number of DWord. Local variables num. Saved. Reg: DWORD ; number of saved registers Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 33

Write. Stack. Frame Example main PROC mov eax, 0 EAEAh mov ebx, 0 EBEBh INVOKE a. Proc, 1111 h, 2222 h exit main ENDP a. Proc PROC USES eax ebx, x: DWORD, y: DWORD LOCAL a: DWORD, b: DWORD PARAMS = 2 LOCALS = 2 SAVED_REGS = 2 mov a, 0 AAAAh mov b, 0 BBBBh INVOKE Write. Stack. Frame, PARAMS, LOCALS, SAVED_REGS Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 34

The Microsoft x 64 Calling Convention • CALL subtracts 8 from RSP • First four parameters are placed in RCX, RDX, R 8, and R 9. Additional parameters are pushed on the stack. • Parameters less than 64 bits long are not zero extended • Return value in RAX if <= 64 bits • Caller must allocate at least 32 bytes of shadow space so the subroutine can copy parameter values Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 35

The Microsoft x 64 Calling Convention • Caller must align RSP to 16 -byte boundary • Caller must remove all parameters from the stack after the call • Return value larger than 64 bits must be placed on the runtime stack, with RCX pointing to it • RBX, RBP, RDI, RSI, R 12, R 14, and R 15 registers are preserved by the subroutine; all others are not. Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 36

What's Next • • • Stack Frames Recursion INVOKE, ADDR, PROC, and PROTO Creating Multimodule Programs Advanced Use of Parameters (optional) Java Bytecodes (optional) Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 37

Recursion • What is Recursion? • Recursively Calculating a Sum • Calculating a Factorial Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 38

What is Recursion? • The process created when. . . • A procedure calls itself • Procedure A calls procedure B, which in turn calls procedure A • Using a graph in which each node is a procedure and each edge is a procedure call, recursion forms a cycle: Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 39

Recursively Calculating a Sum The Calc. Sum procedure recursively calculates the sum of an array of integers. Receives: ECX = count. Returns: EAX = sum Calc. Sum PROC cmp ecx, 0 jz L 2 add eax, ecx dec ecx call Calc. Sum L 2: ret Calc. Sum ENDP Stack frame: Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. ; ; ; check counter value quit if zero otherwise, add to sum decrement counter recursive call View the complete program 40

Calculating a Factorial (1 of 3) This function calculates the factorial of integer n. A new value of n is saved in each stack frame: int function factorial(int n) { if(n == 0) return 1; else return n * factorial(n-1); } As each call instance returns, the product it returns is multiplied by the previous value of n. Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 41

Calculating a Factorial PROC push ebp mov ebp, esp mov eax, [ebp+8] cmp eax, 0 ja L 1 mov eax, 1 jmp L 2 L 1: dec eax push eax call Factorial ; ; (2 of 3) get n n < 0? yes: continue no: return 1 ; Factorial(n-1) ; Instructions from this point on execute when each ; recursive call returns. Return. Fact: mov ebx, [ebp+8] mul ebx ; get n ; eax = eax * ebx L 2: pop ebp ret 4 Factorial ENDP ; return EAX ; clean up stack See the program listing Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 42

Calculating a Factorial (3 of 3) Suppose we want to calculate 12! This diagram shows the first few stack frames created by recursive calls to Factorial Each recursive call uses 12 bytes of stack space. Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 43

What's Next • • • Stack Frames Recursion INVOKE, ADDR, PROC, and PROTO Creating Multimodule Programs Java Bytecodes Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 44

INVOKE, ADDR, PROC, and PROTO • • INVOKE Directive ADDR Operator PROC Directive PROTO Directive Parameter Classifications Example: Exchaning Two Integers Debugging Tips Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 45

Not in 64 -bit mode! INVOKE Directive • In 32 -bit mode, the INVOKE directive is a powerful replacement for Intel’s CALL instruction that lets you pass multiple arguments • Syntax: INVOKE procedure. Name [, argument. List] • Argument. List is an optional comma-delimited list of procedure arguments • Arguments can be: • • immediate values and integer expressions variable names address and ADDR expressions register names Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 46

INVOKE Examples. data byte. Val BYTE 10 word. Val WORD 1000 h. code ; direct operands: INVOKE Sub 1, byte. Val, word. Val ; address of variable: INVOKE Sub 2, ADDR byte. Val ; register name, integer expression: INVOKE Sub 3, eax, (10 * 20) ; address expression (indirect operand): INVOKE Sub 4, [ebx] Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 47

Not in 64 -bit mode! ADDR Operator • Returns a near or far pointer to a variable, depending on which memory model your program uses: • Small model: returns 16 -bit offset • Large model: returns 32 -bit segment/offset • Flat model: returns 32 -bit offset • Simple example: . data my. Word WORD ? . code INVOKE my. Sub, ADDR my. Word Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 48

Not in 64 -bit mode! PROC Directive (1 of 2) • The PROC directive declares a procedure with an optional list of named parameters. • Syntax: label PROC param. List • param. List is a list of parameters separated by commas. Each parameter has the following syntax: param. Name : type must either be one of the standard ASM types (BYTE, SBYTE, WORD, etc. ), or it can be a pointer to one of these types. Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 49

PROC Directive (2 of 2) • Alternate format permits parameter list to be on one or more separate lines: label PROC, comma required param. List • The parameters can be on the same line. . . param-1: type-1, param-2: type-2, . . . , param-n: type-n • Or they can be on separate lines: param-1: type-1, param-2: type-2, . . . , param-n: type-n Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 50

PROC Examples (1 of 3) • The Add. Two procedure receives two integers and returns their sum in EAX. Add. Two PROC, val 1: DWORD, val 2: DWORD mov eax, val 1 add eax, val 2 ret Add. Two ENDP Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 51

PROC Examples (2 of 3) Fill. Array receives a pointer to an array of bytes, a single byte fill value that will be copied to each element of the array, and the size of the array. Fill. Array PROC, p. Array: PTR BYTE, fill. Val: BYTE array. Size: DWORD mov ecx, array. Size mov esi, p. Array mov al, fill. Val L 1: mov [esi], al inc esi loop L 1 ret Fill. Array ENDP Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 52

PROC Examples (3 of 3) Swap PROC, p. Val. X: PTR DWORD, p. Val. Y: PTR DWORD. . . Swap ENDP Read. File PROC, p. Buffer: PTR BYTE LOCAL file. Handle: DWORD. . . Read. File ENDP Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 53

PROTO Directive • Creates a procedure prototype • Syntax: • label PROTO param. List • Parameter list not permitted in 64 -bit mode • Every procedure called by the INVOKE directive must have a prototype • A complete procedure definition can also serve as its own prototype Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 54

PROTO Directive • Standard configuration: PROTO appears at top of the program listing, INVOKE appears in the code segment, and the procedure implementation occurs later in the program: My. Sub PROTO ; procedure prototype . code INVOKE My. Sub ; procedure call My. Sub PROC. . My. Sub ENDP ; procedure implementation Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 55

PROTO Example • Prototype for the Array. Sum procedure, showing its parameter list: Array. Sum PROTO, ptr. Array: PTR DWORD, sz. Array: DWORD ; points to the array ; array size Parameters are not permitted in 64 -bit mode. Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 56

Parameter Classifications • An input parameter is data passed by a calling program to a procedure. • The called procedure is not expected to modify the corresponding parameter variable, and even if it does, the modification is confined to the procedure itself. • An output parameter is created by passing a pointer to a variable when a procedure is called. • The procedure does not use any existing data from the variable, but it fills in a new value before it returns. • An input-output parameter is a pointer to a variable containing input that will be both used and modified by the procedure. • The variable passed by the calling program is modified. Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 57

Trouble-Shooting Tips • Save and restore registers when they are modified by a procedure. • Except a register that returns a function result • When using INVOKE, be careful to pass a pointer to the correct data type. • For example, MASM cannot distinguish between a DWORD argument and a PTR BYTE argument. • Do not pass an immediate value to a procedure that expects a reference parameter. • Dereferencing its address will likely cause a generalprotection fault. Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 58

What's Next • • • Stack Frames Recursion INVOKE, ADDR, PROC, and PROTO Creating Multimodule Programs Advanced Use of Parameters (optional) Java Bytecodes (optional) Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 59

Multimodule Programs • A multimodule program is a program whose source code has been divided up into separate ASM files. • Each ASM file (module) is assembled into a separate OBJ file. • All OBJ files belonging to the same program are linked using the link utility into a single EXE file. • This process is called static linking Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 60

Advantages • Large programs are easier to write, maintain, and debug when divided into separate source code modules. • When changing a line of code, only its enclosing module needs to be assembled again. Linking assembled modules requires little time. • A module can be a container for logically related code and data (think object-oriented here. . . ) • encapsulation: procedures and variables are automatically hidden in a module unless you declare them public Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 61

Creating a Multimodule Program • Here are some basic steps to follow when creating a multimodule program: • Create the main module • Create a separate source code module for each procedure or set of related procedures • Create an include file that contains procedure prototypes for external procedures (ones that are called between modules) • Use the INCLUDE directive to make your procedure prototypes available to each module Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 62

Example: Array. Sum Program • Let's review the Array. Sum program from Chapter 5. Each of the four white rectangles will become a module. This will be a 32 -bit application. Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 63

Sample Program output Enter a signed integer: -25 Enter a signed integer: 36 Enter a signed integer: 42 The sum of the integers is: +53 Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 64

INCLUDE File The sum. inc file contains prototypes for external functions that are not in the Irvine 32 library: INCLUDE Irvine 32. inc Prompt. For. Integers PROTO, ptr. Prompt: PTR BYTE, ptr. Array: PTR DWORD, array. Size: DWORD ; prompt string ; points to the array ; size of the array Array. Sum PROTO, ptr. Array: PTR DWORD, count: DWORD ; points to the array ; size of the array Display. Sum PROTO, ptr. Prompt: PTR BYTE, the. Sum: DWORD ; prompt string ; sum of the array Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 65

Inspect Individual Modules • • Main Prompt. For. Integers Array. Sum Display. Sum Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 66

What's Next • • • Stack Frames Recursion INVOKE, ADDR, PROC, and PROTO Creating Multimodule Programs Advanced Use of Parameters (optional) Java Bytecodes (optional) Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 67

Java Bytecodes • Stack-oriented instruction format • operands are on the stack • instructions pop the operands, process, and push result back on stack • Each operation is atomic • Might be be translated into native code by a just in time compiler Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 68

Java Virual Machine (JVM) • Essential part of the Java Platform • Executes compiled bytecodes • machine language of compiled Java programs Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 69

Java Methods • Each method has its own stack frame • Areas of the stack frame: • local variables • operands • execution environment Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 70

Bytecode Instruction Format • 1 -byte opcode • iload, istore, imul, goto, etc. • zero or more operands • Disassembling Bytecodes • use javap. exe, in the Java Development Kit (JDK) Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 71

Primitive Data Types • Signed integers are in twos complement format, stored in big-endian order Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 72

JVM Instruction Set • Comparison Instructions pop two operands off the stack, compare them, and push the result of the comparison back on the stack • Examples: fcmp and dcmp Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 73

JVM Instruction Set • Conditional Branching • jump to label if st(0) <= 0 ifle label • Unconditional Branching • call subroutine jsr label Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 74

Java Disassembly Examples • Adding Two Integers int int sum A = B = sum = A 3; 2; = 0; + B; Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 75

Java Disassembly Examples • Adding Two Doubles double A = 3. 1; double B = 2; double sum = A + B; Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 76

Java Disassembly Examples • Conditional Branch double A = 3. 0; boolean result = false; if( A > 2. 0 ) result = false; else result = true; Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 77

Summary • Stack parameters • more convenient than register parameters • passed by value or reference • ENTER and LEAVE instructions • Local variables • created on the stack below stack pointer • LOCAL directive • Recursive procedure calls itself • Calling conventions (C, stdcall) • MASM procedure-related directives • INVOKE, PROC, PROTO • Java Bytecodes – another approch to programming Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 78

53 68 75 72 79 6 F Irvine, Kip R. Assembly Language for x 86 Processors 7/e, 2015. 79